Grantee Research Project Results
Synthesis of New Vitamin B12 Model Complexes for Mechanistic Studies of the Reductive Dechlorination of Chlorinated Ethylenes
EPA Grant Number: U916107Title: Synthesis of New Vitamin B12 Model Complexes for Mechanistic Studies of the Reductive Dechlorination of Chlorinated Ethylenes
Investigators: Fritsch, Joseph M.
Institution: University of Minnesota
EPA Project Officer: Lee, Sonja
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $133,716
RFA: STAR Graduate Fellowships (2003) Recipients Lists
Research Category: Fellowship - Chemistry and Materials Science , Academic Fellowships , Safer Chemicals
Objective:
The objectives of this research project are
to: (1) develop a deeper understanding of chlorinated ethylene (CE) reductive
dehalogenation
mechanism by Vitamin B12 through the synthesis of novel model complexes, including
complexes containing new -ketiminate ligands with pendant donor groups; and
(2) study the mechanism of aqueous CE reductive dehalogenation by structurally
similar Vitamin B12 mimics.
Approach:
Synthesis of novel cobalt complexes of new, monoanionic,
tetradentate, aza ligands will supplement existing Vitamin B12 model complexes
and allow
for a new approach to the study of the CE reductive dehalogenation. CEs (perchloroethylene,
trichloroethylene, dichloroethylene, and vinyl chloride) are reductively
dechlorinated by Vitamin B12—a cobalt containing corrin macrocycle, of
which the Co(I) oxidation state is the reactive species. Few cobalt complexes
of monoanionic,
tetradentate, aza ligands have been studied, and new -ketiminate ligands
with pendant donor groups will be used to prepare new complexes. These complexes
will be fully characterized during this research. The complexes will be useful
for investigation into CE degradation. Any isolable Co(I) complexes will
allow
for the study of the individual CE reduction steps. Isolation and characterization
of volatile and inorganic products will be valuable to understanding the
reaction pathway.
In addition, synthetic Vitamin B12 mimics represent an opportunity to find new aqueous reductive dehalogenation catalysts. Cobalt porphyrin complexes have been assessed as viable CE degradation catalysts in batch reactors, and the reduced products were analyzed with gas chromatography with flame ionization detection. Kinetic studies of the factors governing the dehalogenation rate were studied. Also, UV-Vis spectroscopy was used to study the reaction because there are known absorbance maxima for cobalt complexes in different oxidation states. Investigation into the mechanism of catalyst oxidation state cycling and CE degradation pathways currently is underway.
This work will lead to new, highly active dechlorination catalysts with tunable properties, which will make them more useful for engineered dechlorination systems. In addition, the insights gained regarding the dechlorination mechanism may allow for the selective production of nontoxic, benign dechlorination products.
Supplemental Keywords:
fellowship, cobalt complex, chlorinated ethylene, CE, reductive dechlorination, reductive dehalogenation, CE degradation, aqueous reductive dehalogenation catalysts, catalyst oxidation state cycling., RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, INTERNATIONAL COOPERATION, TREATMENT/CONTROL, Waste, Water, Hazardous, Remediation, Restoration, Chemical Engineering, Aquatic Ecosystem Restoration, Environmental Chemistry, Engineering, Chemistry, & Physics, Groundwater remediation, Hazardous Waste, Treatment Technologies, Bioremediation, Environmental Engineering, Technology, reductive dechlorination, vitamin B12, aquifer remediation design, in-situ biotransformation, microbial degradation, biotechnology, bioremediation model, degrade trichloroethylene, groundwater contamination, contaminated aquifers, in-situ bioremediation, aquifer remediation, in situ treatment, hazardous waste treatment, dechlorination, contaminated groundwater, push pull test, dehalogenate, monitoring, groundwater, in situ remediation, biodegradation, bioaugmentation, aquatic ecosystems, groundwater pollution, TCE degradation, reductive dehalogenation, microbiology, redox tools, dehalogenation, TCEProgress and Final Reports:
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.